Variable compression ratio device of internal combustion engine

Abstract

A variable compression ratio device includes a piston having a piston inner part and a piston outer part. The piston outer part integrally includes ear parts facing opposite ends of a piston pin and having long holes with longer diameters directed in an axial direction of a piston. A shaft portion connected to the opposite ends of the piston pin is slidably fitted in the long holes to allow an axial relative movement between the piston inner part and the piston outer part, while preventing relative rotation between the piston inner part and the piston outer part. Thus, the variable compression ratio device reliably prevents the relative rotation between the piston inner part and the piston outer part with a simple structure, and reduces weight of the piston.

1. A variable compression ratio device of an internal combustion engine, comprising:
 a piston including a piston inner part connected to a connecting rod via a piston pin, and a piston outer part which is fitted on an outer periphery of the piston inner part so as to be only slidable in an axial direction and which is movable between a low compression ratio position L near the piston inner part and a high compression ratio position H near a combustion chamber, with an outer end surface of the piston outer part facing the combustion chamber, 
 the piston inner part being provided with a piston outer part holding device that selectively holds the piston outer part in the low compression ratio position L and the high compression ratio position H, 
 wherein long holes with longer diameters directed in an axial direction of the piston are provided in the piston outer part to face opposite ends of the piston pin; and a shaft portion connected to the opposite ends of the piston pin is slidably fitted in the long holes to allow an axial relative movement between the piston inner part and the piston outer part while preventing relative rotation between the piston inner part and the piston outer part. 
 
   
   
     2. The variable compression ratio device of an internal combustion engine according to  claim 1 , wherein the shaft portion is abutted against lower end walls of the long holes to establish a movement limit of the piston outer part toward the high compression ratio position H. 
   
   
     3. The variable compression ratio device of an internal combustion engine according to  claim 1 , wherein the long holes are provided in a pair of ear parts extending from a peripheral wall of the piston outer part that receives piston rings so as to face the opposite ends of the piston pin; and a skirt portion slidably guided by an inner peripheral surface of a cylinder bore is formed integrally with the piston inner part and away from the ear parts. 
   
   
     4. The variable compression ratio device of an internal combustion engine according to  claim 1 , wherein an inner slide flat surface extending in an axial direction of the piston is formed in an outer peripheral surface of the piston inner part; and an outer slide flat surface against which the inner slide flat surface slidably abuts is formed in an inner peripheral surface of the piston outer part. 
   
   
     5. The variable compression ratio device of an internal combustion engine according to  claim 3 , wherein inner slide flat surfaces extending in an axial direction of the piston are formed in opposite sides of the outer peripheral surface of the piston inner part that face the opposite ends of the piston pin; and outer slide flat surfaces against which the inner slide flat surfaces slidably abut are formed in inner surfaces of the ear parts. 
   
   
     6. The variable compression ratio device of an internal combustion engine according to  claim 2 , wherein a shock absorber that absorbs an abutment shock of the shaft portion abutting against the lower end walls of the long holes is provided between the shaft portion and the piston inner part. 
   
   
     7. The variable compression ratio device of an internal combustion engine according to  claim 1 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     8. The variable compression ratio device of an internal combustion engine according to  claim 2 , wherein an escape is provided in an inner end of the lower end wall of each long hole on the side of the center of the piston outer part, the escape preventing the shaft portion from coming into contact with an inner end corner of the lower end wall on the side of the center of the piston outer part when the shaft portion is bent by an abutment shock against the lower end wall. 
   
   
     9. The variable compression ratio device of an internal combustion engine according to  claim 8 , wherein the lower end wall of each long hole comprises a semicylindrical wall that has one end connected to an outer peripheral surface of the piston outer part and corresponds to a half of a peripheral surface of the shaft portion, and a semi-conical wall that extends from the other end of the semicylindrical wall to an inner peripheral surface of the piston outer part and has a diameter increasing toward the inner peripheral surface; and the semi-conical wall forms the escape. 
   
   
     10. The variable compression ratio device of an internal combustion engine according to  claim 2 , wherein the long holes are provided in a pair of ear parts extending from a peripheral wall of the piston outer part that receives piston rings so as to face the opposite ends of the piston pin; and a skirt portion slidably guided by an inner peripheral surface of a cylinder bore is formed integrally with the piston inner part and away from the ear parts. 
   
   
     11. The variable compression ratio device of an internal combustion engine according to  claim 2 , wherein an inner slide flat surface extending in an axial direction of the piston is formed in an outer peripheral surface of the piston inner part; and an outer slide flat surface against which the inner slide flat surface slidably abuts is formed in an inner peripheral surface of the piston outer part. 
   
   
     12. The variable compression ratio device of an internal combustion engine according to  claim 2 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     13. The variable compression ratio device of an internal combustion engine according to  claim 3 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     14. The variable compression ratio device of an internal combustion engine according to  claim 4 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     15. The variable compression ratio device of an internal combustion engine according to  claim 5 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     16. The variable compression ratio device of an internal combustion engine according to  claim 6 , wherein the piston outer part holding device includes a lift member that is rotatably supported by and coaxially with the piston inner part and is rotatable between a lift release position A in which the piston outer part is movable to the low compression ratio position L, and a lift position B in which the piston outer part is held in the high compression ratio position H. 
   
   
     17. The variable compression ratio device of an internal combustion engine according to  claim 3 , wherein an escape is provided in an inner end of the lower end wall of each long hole on the side of the center of the piston outer part, the escape preventing the shaft portion from coming into contact with an inner end corner of the lower end wall on the side of the center of the piston outer part when the shaft portion is bent by an abutment shock against the lower end wall.